When the human heart stops beating, death can occur within a matter of minutes, for example, in an average case, seven minutes.
First aid techniques have been developed for compressing the heart, in which the patient's chest wall is cyclically pressed down and released, by hand.
To be effective, this treatment must often be repeated at about sixty pumps per minute for a period as long as possible until help arrives. Unless the one rendering first aid is in good condition such treatment may not be sustainable and may be hazardous to the one rendering first aid.
Even if the one rendering first aid is in good condition, over a period of sustained exertion the motion may not continue in an optimum direction or with optimum force. Training varies, as do the abilities of the trainees.
All in all, the manual method of heart compression leaves much to chance, and it is known by the inventor that elaborate and complex and costly equipment has been sold for the purposes herein, but of a different design and operation.